The invention relates to a composite compressed gas tank that is intended for a gas and that has an outer shell and a liner, which is enveloped by said outer shell and which is made of a light metal, in particular, aluminum or an aluminum alloy, and which has an infeed and discharge port, in which is inserted a closing element having at least one channel for infeeding and/or discharging gas. Such a tank can be used, for example, in a motor vehicle in order to store a compressed natural gas (CNG) or hydrogen, for instance, also in the cryogenic state, as the energy carrier for the vehicle drive unit or for an auxiliary power unit.
The well-known composite compressed gas tanks that are, for example, bottle-shaped and have aluminum liners, are distinguished by a relatively low weight and are, therefore, quite suitable for the storage of compressed gas in vehicles. A newer development goes in the direction of storing cryogenic hydrogen under pressure in the supercritical state as the energy carrier for the drive unit of a vehicle. Under certain operating conditions the stored hydrogen can have a temperature of 35 Kelvin, whereas under other operating conditions pressure values in a magnitude of 300 bar and more can prevail in the pressure tank system. At the same time the goal is to minimize as much as possible any undesired thermal input from the environment into the compressed gas tank.
As well-known, a heat exchange occurs simultaneously over the connecting lines of a compressed gas tank, which is loaded or unloaded by way of these connecting lines. That is, heat is brought into the interior of the compressed gas tank from the environment over these connecting lines, which contain a channel or channels for the infeed of gas into the compressed gas tank or for the discharge of gas from the compressed gas tank. Therefore, with respect to reducing the heat input into the compressed gas tank, the materials that are used for these connecting lines should exhibit a relatively low thermal conductivity (while simultaneously exhibiting adequate strength). Therefore, these connecting lines may be made preferably of stainless steel.
With respect to the aforementioned high pressure values, the connections between the individual lines of the connecting line system and between the connecting line(s) and the aluminum liner of the compressed gas tank must also be configured so as to be absolutely pressure tight, for which reason virtually only a welded joint is suitable for such connections. However, stainless steel as a material is not easily weldable with aluminum.
Therefore, there is needed a composite compressed gas tank comprising a liner, which is made of a light metal, in particular aluminum, and to which can be welded in a relatively easy way the connecting lines or a connecting line made of a steel material, in particular stainless steel.
The need is met by a composite compressed gas tank with an outer shell and a liner, which is enveloped by said outer shell and which is made of a light metal, in particular, aluminum or an aluminum alloy, and which has an infeed and discharge port, in which is inserted a closing element that has at least one channel for infeeding and/or discharging gas and that is connected directly or indirectly to the liner by a welded joint. A connecting line made of a steel material is connected to the channel or channels of the closing element. There is a transition element having a first end segment made of a light metal, in particular aluminum or an aluminum alloy, that is welded either to the liner or to the closing element, which is made of a light metal, in particular aluminum or an aluminum alloy. Another end segment of this transition element is made of a steel material. This other end segment is welded either to the closing element, which is made of a steel material, or to the connecting line, which is made of a steel material.
The invention provides a so-called transition element, through which the channel or channels, continuing in the connecting line, is (are) guided directly or indirectly, that is, with the interposition of another structural element. The two end segments of this transition element are made of different materials, that is, aluminum or a weldable aluminum alloy, on the one hand, and steel, preferably stainless steel, on the other hand.
Thus, it is possible to weld in a relatively easy way this transition element with its first end segment to an aluminum component of the compressed gas tank module that is formed by the compressed gas tank, its closing element and the connecting line, whereas the second end segment of the transition element that is made of steel can be welded in a relatively easy way to a structural element, which is made of a steel material and which is a part of the module, formed by the compressed gas tank, its closing element and the connecting line.
The so-called transition element, of which an aluminum end segment is connected to a (stainless) steel end segment, can be manufactured by means of especially suitable production methods. In this case a manufacturing intensive welded joint between steel, on the one hand, and aluminum, on the other hand, is preferred for safety reasons and tightness reasons. On the other hand, such expensive welded joints, such as preferably friction welding or explosion welding, at a separate transition element can still be implemented in a relatively simple way, as long as there are no other components, like the compressed gas tank itself or the connecting line(s), in the vicinity or as long as such other components do not have to be considered. In particular, owing to the high pressure conditions that have to be maintained when the compressed gas tank of the invention is operating, it can be advisable to provide a clamping element that surrounds the transition element, in particular in the abutting area and/or the joining area of the two materials (that is, aluminum and steel).
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.